In recent years, a large amount of digital data including audio data and video data has been used for digital communication. Therefore, the audio data and the video data need to be transmitted in the form of compressed digital data. The audio data is called a compressed digital audio stream. When the audio data is received, it is separated from the video data. Then, the audio data is decompressed and decoded and is then converted into analog data. In this way, the audio data can be played as a sound.
When the compressed digital audio stream is an MPEG (Moving Picture Expert Group) audio having a sampling frequency of 48 kHz, it is separated from the video data and is then decoded. Then, the compressed digital audio stream is converted into a frame having plurality of PCM (Pulse Coded Modulation) data corresponding to a time of 24 ms. When defect occurs in the compressed digital audio stream, such as when audio data in the compressed digital audio stream is not duly received, the PCM data could not be generated, which causes a defect in a frame, such as the omission of the frame including the PCM data.
In this case, a method of generating a frame composed of PCM data having a level of zero is used to complement the defect in a frame. However, in this method, reproduced audio data varies discontinuously, which causes a sound noise, such as a pop sound or a click sound. As a result, sound quality deteriorates. In order to solve this problem, a method of using a filter to convert the discontinuous audio data into audio data having smooth audio waveform has been disclosed. However, since this method causes an increase in the amount of computing data, the method is not practical. As another solution, a method of complementing an omitted frame with the frame recorded immediately before the omission occurs has been proposed (for example, see JP-A-9-027757 (U.S. Pat. No. 5,732,736)).